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Beneath the waves, this so-called spacecraft cemetery has 161 residents, Kiona Smith-Strickland reports for Gizmodo. The spot was selected for its isolation, tar from land and low on shipping traffic, so that no unsuspecting humans might be injured when the crafts plunge into the deep water. Some of the spacecraft cemetery's residents include cargo crafts from Japan, Europe and Russia, as well as space stations. Russia's Mir station arrived in 2001.

"There’s a lot of space history down there, but of course, none of these spacecraft are just sitting neatly on the ocean floor in one piece. Or even two pieces," Smith-Strickland writes. "Re-entering the Earth’s atmosphere is a violent, destructive process for any object that tries it, whether it’s a meteor or a space station."

Many small, lower orbiting satellites burn up when they hit the Earth's atmosphere. Larger stuff — bigger satellites, autonomous spacecrafts and maybe one day the International Space Station — would break into pieces but probably wouldn't completely burn to smithereens before hitting the ground. In Mir's case, while the original craft weighed 143 tons, only around 20 tons made it to the Pacific. Satellite operators and space agency scientists can program their crafts to reach this area upon reentry, but it's not an exact target.

The ESA's Jules Verne ATV (or automated transfer vehicle) re-enters Earth's atmosphere in a controlled burn-up after undocking from the International Space Station. It now resides in the spacecraft cemetery.
(NASA/ESA/Bill Moede &Jesse Carpenter)

But, the spacecraft graveyard of the Pacific isn't their only available resting place. When a spacecraft comes to the end of its useful life, scientists at NASA and other space agencies have two options: Shoot it so far out into space that it won't come back or use its last remaining fuel to return it to Earth. NASA and other agencies came to agreement to dispose of dead spacecrafts either in graveyard orbit or in a watery grave in 1993, in an effort to reduce the amount of non-working debris (aka space junk) orbiting the Earth.

With the first option, it's possible to blast a satellite from its orbit further into space into what NASA calls a "graveyard orbit." That's 22,400 miles above earth and roughly 200 miles from the furthest active satellites. Out there it takes more than one Earth day for a satellite to complete its orbit.

This method is often preferrable — graveyard orbit requires less gas and is sometimes the easier route. Blasting upward only requires a velocity of merely .006 miles per second, while sending a satellite back toward Earth's atmosphere demands a bigger push of about a mile per second, as Mika McKinnon reported for io9 last year.

But as McKinnon (and others) have pointed out, in some ways, shooting dead spacecrafts further into space is just a temporary fix. The graveyard satellites add to the growing amount space junk that orbits the Earth. While the Pacific cemetery requires more fuel, it cuts some of the trash in the burn-up. This junk runs the small risk of crashing into other spacecrafts, whether dead or alive, thus damaging working satellites and creating more space junk — which someone might have to clean up one day.

But, hey, that sounds like a problem for future Earth residents.

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About Helen Thompson

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.